Today, we find a cannon that's 200 years older than
it ought to be. The University of Houston's College
of Engineering presents this series about the
machines that make our civilization run, and the
people whose ingenuity created them.

For years we thought the
oldest cannons were late medieval bombards.
Bombards were big cast-iron pots. The French called
them pots de fer -- literally, "pots
of iron." They were pear-shaped with a narrow neck
and a flared top. The oldest one on record shows up
in a French manuscript written in 1327. It fired a
projectile shaped like a spear.

Historians have argued over the source of firearms.
Before 1327 one finds ambiguous hints of Arabic,
Chinese, and European guns. The remains of a
Chinese handgun date to 1288 -- only 39 years
before that French bombard. Old writings in the
West mention ordnance that might have used
explosives. But, at best, they too go back only
into the late 1200's.

In 1985 a visitor to a Buddhist cave in the Chinese
province of Szechuan noticed something that other
people had missed. There, carved on opposing walls,
are groups of men, armed to the teeth. One is a
demon-like fellow, holding what is unmistakably a
bombard -- just like the one in the French drawing.
Another holds a bomb. Both carvings are unambiguous
-- they even show flames exploding outward.

But there's a catch. These figures were carved in
1128 -- two centuries before the French
bombard.

Historians Lu, Needham, and Phan take this as
pretty solid evidence that the cannon went from
China to Europe. But why did anything so important
take so long to make the trip? They come to an odd
conclusion. You need a lot of saltpeter to make
good gunpowder, and the best source of medieval
saltpeter was animal manure. China didn't have as
many domesticated animals as Europe, so saltpeter
was harder to come by. Chinese gunpowder didn't
have enough saltpeter in it, and it wasn't very
powerful. The bombard didn't spread very rapidly in
China because the Chinese used weak explosives.

The last crowning irony of these carvings is the
intent of the cave itself. It's meant to propagate
its builders' prayers for permanent peace -- their
prayers "that weapons of war be forever stilled."
The figures on the walls display all the weapons
that the sculptors wanted never to be used.

Yet the new state-of-the-art bombards eventually
came out of the cave and out of China. Western
armorers loaded them with powerful explosives and
made them into a terrible weapon. This 850-year-old
prayer for permanent peace reveals the beginnings
of slaughter on a scale those Buddhist monks could
never have imagined.

I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.